In-situ surfactant and chemical oxidant flushing for complete remediation of contaminants and methods of using same

ABSTRACT

The present invention relates to removal of subsurface contaminants and methods of same. In more particular, but not by way of limitation, the present invention relates to an integrated method for remediating subsurface contaminants through the use of a low concentration surfactant solution (and methods of making and using novel surfactant solutions).

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. Ser. No. 11/054,582, filedFeb. 9, 2005, which is a continuation of U.S. Ser. No. 10/294,424, filedNov. 6, 2002, which claims the benefit under 35 U.S.C. §119(e) of U.S.Provisional Application Ser. No. 60/333,244, filed Nov. 11, 2001,entitled “USE OF IN-SITU SEQUENT AND CHEMICAL OXIDANT FLUSHING FORCOMPLETE REMEDIATION OF CONTAMINATED SOILS AND GROUNDWATERS”, thecontents of which are expressly incorporated herein in their entirety byreference.

BACKGROUND

1. Field of the Invention

The present invention relates to removal of subsurface contaminants andmethods of same. In more particular, but not by way of limitation, thepresent invention relates to an integrated method for remediatingsubsurface contaminants through the use of a low concentrationsurfactant solution (and methods of making and using novel surfactantsolutions) followed by an abiotic polishing process to thereafterachieve a substantially reduced subsurface contaminant concentrationthat surfactant flushing alone cannot achieve.

2. Background Information Relating to the Invention

Surfactant enhanced subsurface remediation (SESR) is a unique technologyfor expediting subsurface remediation of non-aqueous phase liquids(NAPLs). Studies known to those in the art have previously evaluated theSESR technology in both laboratory scale studies and field scaledemonstration studies. Traditionally, the surfactant system in SESR(typically an anionic or nonionic surfactant), is designed to removeorganic contaminants (including chlorinated solvents) from contaminatedthe soil. Surfactant systems significantly increase the solubility ofhydrophobic organic compounds and, if properly designed and controlled,also significantly increase the mobility of NAPLs. A significantlyreduced remediation time thereby results as well as increased removalefficiency (up to 3 or 4 orders of magnitude) and reduced cost of NAPLremoval through use of surfactant system for subsurface remediation.

Surfactant flushing solutions, typically, can be designed to beeffective under most subsurface conditions. In most cases, theeffectiveness of the surfactant flushing solutions is not reduced due tothe presence of more than one contaminant. Naturally-occurring divalentcations and salts may affect the performance of certain surfactants, aswell as the removal efficiency for cationic heavy metals. It ispossible, however, to design an effective surfactant system for removalof the target contaminants under any of these conditions. A number offactors influence the overall performance and cost effectiveness of SESRsystems. These factors include: Local ground water chemistry; Soilchemistry (e.g. sorption, precipitation); Ability to deliver thesurfactant solution to the area of contamination; Surfactant effects onbiodegradation of the NAPL compounds as well as degradation of thesurfactants; Public and regulatory acceptance; Cost of the surfactant;Recycle and reuse of the surfactant, if necessary; and Treatment anddisposal of waste streams. Bench scale tests (treatability studies) mustbe conducted on site specific soils and NAPL (if available) to ensurethe optimal system is selected for a particular site.

Surfactant flushing can remove a large portion of the mass of subsurfacecontaminant liquid. In general, it is not expected that surfactantflushing alone will have a high probability of reducing the subsurfacecontaminant concentration to a level necessary to allow the site to beconsidered “remediated.” Therefore, a treatment train (or integrated)approach is necessary to speed up or achieve the closure of the site. Itis to such an integrated approach involving a preselected surfactantsolution flush coupled with an abiotic oxidation polishing step andmethods thereof that the present invention is directed.

SUMMARY OF INVENTION

The present invention is directed to a method for substantially removingsubsurface contaminants through an integrated approach utilizing apreselected surfactant solution and a preselected chemical oxidant. Suchan innovative integrated approach satisfies a need in the marketplacefor a cost-effective and less time consuming system to removesubstantially all subsurface contaminants—a level of remediation hasbeen traditionally unavailable. A method of the present inventioncomprises the steps of introducing an effective amount of at least onepreselected surfactant solution and an effective amount of at least onepreselected chemical oxidant. The combination of the preselectedsurfactant solution and the preselected chemical oxidant are capable ofsubstantially removing subsurface contaminants. Additionally, thepresent invention relates to a subsurface contaminated site that issubstantially remediated by this integrated approach and novelsurfactant solutions.

DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 is a schematic diagram showing, generally, an integratedsurfactant flushing and treatment system according to the presentinvention.

FIG. 2 is a graphical representation showing the results of a NAPLremoval test in a one-dimensional (1-D) column.

FIG. 3 is a schematic representation of pre- and post-surfactant freephase gasoline distribution in a “Shallow Zone” at an undergroundstorage tank contamination site—i.e. Carroll's Grocery in Golden, Okla.

FIG. 4 is a schematic representation of pre- and post-surfactantflushing/chemical oxidation benzene concentration distributionmethodology of the present invention in a “Shallow Zone” at anunderground storage tank contamination site—i.e. Carroll's Grocery inGolden, Okla.

FIG. 5 is a graphical representation showing the results of a TCEbreakthrough test with sequent surfactant and chemical oxidationflushing in a 1-D column.

DETAILED DESCRIPTION OF INVENTION

It is to be understood that the invention is not limited in itsapplication to the details of construction and the arrangements of thecomponents set forth in the following description (e.g. texts, examples,data and/or tables) or illustrated or shown in the drawings. Theinvention is capable of other embodiments or of being practiced orcarried out in various ways. Also, it is to be understood that thephraseology and terminology employed herein is for purpose ofdescription and should not be regarded as limiting and one of ordinaryskill in the art, given the present specification, would be capable ofmaking and using the presently claimed and disclosed invention in abroad and non-limiting manner.

As used herein, the term “subsurface contaminant” refers to any organicor inorganic impurity or halogenated solvent (such as a chlorinatedsolvent) that is toxic to the underground surface. Additionally, theterm “surfactant solution” refers to any anionic or nonionic surfactantor cosurfactant combination that is functionally capable of removingorganic or inorganic contaminants as well as halogenated solvents (suchas a chlorinated solvent) from a contaminated subsurface area, such assubsurface soil or water systems. Further, the term “oxidant” refers toany oxidizing agent capable of degrading a contaminated plume orentrapped residual pollutants whether they are organic, inorganic, orhalogenated solvents. The term “polishing step” as used herein, refersto the innovative abiotic process of the presently disclosed and claimedinvention that includes the steps of injecting or introducingpredetermined concentrations of a chemical oxidant to further degradeand reduce the subsurface contaminant subsequent to a surfactantflushing step. “Integrated approach” as used herein, refers to a lowconcentration surfactant flush in combination with the abiotic polishingstep. “Remediation” as used herein, refers to the substantially completeremoval of soil and groundwater pollutants by various treatments orrestoring methods to achieve the standard set by the responsibleregulatory agency for the particular contaminated subsurfact system(e.g. National Primary Drinking Water Regulations (NPDWR) for subsurfaceground water).

Due to certain advantages associated with the use of the integratedapproach of the presently claimed and disclosed invention, one ofordinary skill in the art will most likely recognize the benefits ofthis approach when time is of the essence. One such advantage is that byusing the low concentration surfactant flush step in combination withthe subsequent abiotic polishing step, a higher probability exists ofreducing the subsurface contaminant concentration to a level necessaryto allow the site to be considered remediated—i.e. substantially allcontaminats have been removed. This process will tend to achieve minimalpollutant content of the underground surface while decreasing the timespent as compared to prior art techniques that utilize a higherconcentration surfactant flush as the sole means of remediating acontaminated site.

Prior to Applicant's inventive concept, higher concentration surfactantflushing alone has been the common method of site remediation. As shownin FIG. 1, the present invention includes an overall integratedsurfactant flushing and treatment system 10. A pre-determined surfactantsolution 20 is prepared in a mixing tank 30. After the surfactantsolution 20 is prepared, the surfactant-NAPL phase behavior is evaluatedon-site. If the surfactant solution 20 meets all criteria set for thesurfactant—NAPL phase behavior, such as optimal microemulsion (eitherWinsor Type III or Type I) the surfactant solution 20 is delivered to atargeted treatment zone 40 via an injection well 50 and a pumping system60. Removed contaminant and surfactant solution 70 is extracted from arecovery well 80. The free-phase oil is separated from the surfactantstream in an oil/water separator 90. If the contaminant and surfactantsolution 70 is pH sensitive for its recovery, a pH-adjustment tank 100could be added before the oil/water separator 90 to reduce the solutionpH and enhance the surfactant separation. From the oil/water separator90, a waste stream 110 is sent to an air stripper 120 or other equipment(such as liquid-liquid extraction) to remove dissolved volatile organicchemicals (VOC) 130. The waste stream 110 is delivered to apre-filtration system 140 to remove the large solid particle or sedimentin the waste stream 110. If surfactant reuse is required, the wastestream 110 will go through a second pH-adjustment tank 150 and anultrafiltration membrane system 160. Most surfactant micelle phase willbe rejected at the retentate side 170 and sent back to the mixing tank30 for reuse. The waste water containing mainly surfactant monomer andtrace contaminant will pass through the ultrafiltration membrane system160 for final disposal 180 or sent to a wastewater treatment plant fortreatment.

As outlined and shown in particular examples hereinafter, theApplicant's presently claimed and disclosed methodology demonstratessignificant removal of NAPL from a contaminated source area viaremediation. In one embodiment of this invention, surfactant flushingprojects were conducted at a surfactant concentration ranging between 3to 8 wt % of surfactant based upon the total weight of the surfactantsolution (e.g. 3 wt % would be 3% surfactant/97% water or othersolvent). This range may be somewhat over-conservative because, withinthis range of surfactant concentrations, reuse or reconcentration of therecovered surfactant typically is necessary to improve the economics ofthe overall project. In order to recover/separate the surfactant,contaminant concentrations must be reduced to acceptable levels in thesurfactant solution and then the surfactant must be re-concentrated forreinjection. In other embodiments of this invention, surfactantconcentrations in a range from about, 0.05% to about 15 wt % arecontemplated for use. In a most preferred embodiment of this invention,a lower surfactant concentration, such as 0.1%, is most desirable.Several advantages of using a low surfactant concentration, are: (1)significant savings on chemical use and project cost; (2) minimizingand/or completely eliminating the reuse and recycling of the recoveredsurfactant; and (3) improving the above-ground treatment efficiency(e.g., less retention time for breaking the macro- or microemulsionduring the oil/water separation stage, and less foaming of surfactant).Therefore, the ability of lowering the costs of a SESR project, such aswith utilizing a lower surfactant concentration, further improves thetotal cost effectiveness for the remediation of sites. The quantity ofsurfactant necessary for use with the presently disclosed and claimedinvention is up to one order of magnitude (from several weight percentsreduced to several thousands ppm or mg/L) less than prior art surfactantflushing systems used for light non-aqueous-phase liquids (LNAPLs) aswell as for dense non-aqueous phase liquids (DNAPLs).

The surfactant solution of the presently claimed and disclosed inventionmay be any anionic, cationic, or nonionic surfactant or any combinationsthereof as well as one or more combinations thereof. These combinationsinclude, but are not limited to: anionic surfactant/anionic surfactant;anionic surfactant/nonionic surfactant; anionic surfactant/cationicsurfactant; nonionic surfactant/nonionic surfactant; and nonionicsurfactant/cationic surfactant combinations, to name but a few of thepossible permentations.

Further, the present invention encompasses an abiotic process to addressthe post-surfactant polishing step to further enhance site remediation.This abiotic process involves injecting pre-determined concentrations ofchemical oxidant to degrade the dilute contaminant plume and/or traceentrapped residual pollutant(s) that remain after the surfactantflushing step. The effectiveness of these oxidants depends on the typesof contaminants and geological formations found at the site. Thus, thechemical oxidant is chosen or “predetermined” based on an analysis ofthe site: i.e. the functionality of the chemical oxidant must match orbe capable of degrading any remaining contaminants or pollutants. Thus,one of ordinary skill in the art, given the present specification, wouldbe capable of selecting an appropriate chemical oxidant given anidentification of the contaminants or pollutants to be remediated.

The two most common oxidizing agents used for in-situ chemical oxidationare hydrogen peroxide and potassium permanganate, yet various otheroxidizing agents including, but not limited to, sodium permanganate,ozone, chlorine dioxide, or dissolved oxygen may be used. In thechemical oxidation process known as Fenton's reaction, injection ofhydrogen peroxide is typically combined with an iron catalyst underreduced pH conditions to generate powerful hydroxyl free radicals (OH).Since 1934, Fenton's reagent has been recognized as an effective meansfor destroying organic compounds in wastewater and most recently as anin-situ treatment method for soil and groundwater. The dissolved ironacts as a catalyst for generating the hydroxyl radical, resulting infree-radical oxidation of the contaminant. A low pH is necessary to keepthe iron in the ferrous state. While the reaction can be performedsuccessfully at a pH range between 5 and 7, the performance improves ateven lower pH values (as low as 2 to 3). Obtaining optimal subsurface pHconditions is often limited by the soil buffering capacity, which issite-specific. For example, if naturally-occurring carbonates in thesoil are high, a significant acid dose is required to reduce the pH atthe site and thereby improve the performance of the oxidizing agent.

Potassium permanganate oxidation creates little heat or gas, thereforecontaminant treatment occurs primarily through oxidation. Potassiumpermanganate is an oxidizing agent with a unique affinity for organiccompounds containing carbon-carbon double bonds, aldehyde groups orhydroxyl groups. Under normal subsurface pH and temperature conditions,the primary oxidation reaction for perchloroethylene (PCE) andtrichloroethylene (TCE) involves spontaneous cleavage of thecarbon-carbon bond. Once this double bond is broken, the highly unstablecarbonyl groups are immediately converted to carbon dioxide througheither hydrolysis or further oxidation by the permanganate ion.Selection of the proper oxidant is based on several factors including,but not limited to, contaminant characteristics, site geochemicalconditions, soil buffering conditions of site, and etc. Fenton's reagentis capable of oxidizing a wide range of compounds while potassiumpermanganate is more selective and is best suited for chlorinated ethenecontaminants such as PCE and TCE. Potassium permanganate often providesmore rapid destruction of specific compounds when compared to Fenton'sreagent, however.

Previous prior art results from field tests raised concerns on theeffectiveness of using chemical oxidation for contaminated source zoneremediation. Mainly, this was due to the high concentration of oxidantrequired, the large amount of heat and gas released in the subsurface,and the formation of solid-precipitate at the surface of the contaminantliquid pool. Utilizing the presently disclosed and claimed methodology,however, the bulk of the contaminant has been previously removed bysurfactant flushing, followed by a very low concentration (preferrablyless than 0.5 wt %) of oxidant can be used, and the amount of heatgenerated and the volume of gas released ceases to be a limiting factor.Using the methodology of the presently claimed and disclosed invention,surfactant flushing followed by chemical oxidation is highly effectivefor contaminant remediation. Thus, neither surfactant flushing norchemical oxidation alone can accomplish substantially, one hundredpercent remediation of a contaminated site. The combination ofsurfactant flushing followed by chemical oxidation does, however, resultin a substantially remediated site that had been contaminated prior totreatment. The presently disclosed and claimed methodology greatlyreduces the long-term risk and financial burden of the owner of thecontaminated site in a site closure program versus a maintenance-likeapproach such as pump-and-treat. The uniqueness of the presently claimedand disclosed integrated process approach provides significantimprovement on the NAPL clean-up efficiency as compared to thestand-alone surfactant flushing and stand alone in situ chemicaloxidation for site remediation effort.

Experiment Methodology

Surfactant Selection and System Design. Selection of the propersurfactant system utilizing a series of laboratory screening tests isone of the most crucial steps in conducting a successful surfactantflushing project. Laboratory surfactant screening typically consists ofthe following tests: contaminant solubilization tests, surfactant-NAPLphase behavior properties tests, surfactant sorption and precipitationtests, and contaminant extraction-column studies. Representativeprocedures of these tests are briefly described below. One of ordinaryskill in the art, however, would appreciate the significance and stepsnecessary to conduct such tests given the present specification. Thepurpose of these tests is to select the best surfactant system forapplication at the site—the surfactant is optimized for both thephysical and chemical conditions of the site and the contaminant.

Contaminant solubilization of NAPL Solubilization tests are used todetermine the solubilization capacity of the surfactant systems (seee.g. Shiau et al., 1994; Rouse et al. 1993). For a DNAPL contaminant,the objective of the solubilization test is to select a surfactantsystem with ultra-solubilization potential without mobilizing the NAPL.For a LNAPL contaminant, the optimal surfactant system is chosen basedon mobilization of NAPL under the ultra-low interfacial tensioncondition. Typically, surfactant systems under such conditions willproduce a so-called Winsor Type III (or the middle phase) microemulsionvia testing of surfactant-NAPL phase behavior properties (Shiau et al.,1994). The solubilization capacity of site-specific NAPL is determinedfor the surfactants by two methods: direct visual observation (see Shiauet al., 1994) and gas chromatography/flame ionization detector (GC/FID)(i.e., EPA Method 8015 for gasoline range organics (GRO), diesel rangeorganics (DRO), and other volatile organic chemicals (VOCs)) and/or gaschromatography/photoionization detector (GC/PID) measurement (i.e., EPAMethod 8021B for BTEX compounds). Direct visual observation is used as apreliminary screening tool for various surfactant and NAPL systems. Whena proper surfactant/cosurfactant system is utilized, a middle-phasemicroemulsion (a translucent liquid phase intermediate between the waterand NAPL phases) is observed in a mixture of surfactant and NAPL system.

Surfactant-NAPL phase behavior properties. The difference between amicroemulsion and macroemulsion (or emulsion) is that a microemulsion isthermodynamically stable while a macroemulsion is thermodynamicallyunstable and will ultimately separate into oil and water phases.Typically, a macroemulsion of NAPL and surfactant mixture appears opaqueafter equilibration. During the surfactant-NAPL phase behavior testing,equal volume of NAPL and surfactant solution was added to a batchreactor (at capacity between 10 mL to 40 mL) and the system was adjustedwith salt (NaCl), hardness (CaCl₂), or cosolvent (short chain alcohols)to change the hydrophobicity, a crucial parameter to achieve the optimalsurfactant phase behavior, of NAPL and surfactant mixture. The solutionwas shaken and left to equilibrate at room temperature (18° C.)following a 24-hour pre-mixing period. Formation of a stablemiddle-phase microemulsion becomes complete within a few hours to oneday. The presence of a middle-phase microemulsion is confirmed by visualobservation (formation of a translucent liquid) and instrumentation(measuring the ultra-low interfacial tension (IFT) with a spinning droptensiometer). (See Cayias et. al, 1975; Shiau et. al, 2000).

Sorption, Precipitation, and Phase Behavior Analyses. These tests assessthe potential for surfactant losses under subsurface conditions (seeShiau et al., 1995 for details). Surfactants can be lost due tosorption, precipitation, and adverse phase behavior reactions. Excesssurfactant sorbed or precipitated onto soil inhibits systemeffectiveness and increases costs. Sorption testing quantifies theamount of surfactant lost to soil and facilitates a surfactantcomparison analysis. Some surfactants may precipitate or phase separatedue to the presence of salts, divalent cations or temperaturefluctuations. It is essential to ensure that the surfactant will notprecipitate under site specific aquifer conditions. Surfactant loss dueto precipitation and/or phase separation not only hinders performancebut also plugs the aquifer. Formation of an opaque solution in a mixtureof NAPL/surfactant indicates an adverse phase behavior, which does notprovide a satisfactory sweep efficiency and/or solubilization capacityin the subsurface.

Contaminant Extraction-Column Studies. One-dimensional (1-D) columntests are conducted to simulate flow through conditions in the aquifer(see Shiau, et al., 2000 for detailed procedures). Although it isdifficult to simulate actual site conditions, valuable information canbe obtained from column studies. This information includessolubilization enhancement under continuous flow conditions and headlosses during flushing through the media.

The results of the column studies aid in the design of pilot andpotential full-scale application designs of the presently claimed anddisclosed inventive methodology. Column test results are used toquantify the number of pore volumes (PV) required to mitigate the NAPLfor each surfactant system and the polishing step. Previous laboratoryand field studies indicate that the solubilization mechanism requires3-15 PV for most NAPL mass recovery (Shiau, et al. 2000). For themobilization mechanism, the required surfactant solution flush isbetween one to two pore volumes (PV) to recover the majority of the NAPLmass. From site soil-packed columns, residual saturation is achieved inthe column by adding the site-specific contaminant(s) to the column(between 0.01 to 0.2 PV) followed by water to remove excess contaminant.A mass balance of NAPL is determined to estimate the residualconcentration.

Under low surfactant concentration conditions (<1 wt % of surfactant),reuse and recycling of surfactant is economically unnecessary forfull-scale implementation. If injection of a higher concentrationsurfactant is necessary at the particular site, one of ordinary skill inthe art could use membrane-based systems, such as Micellar EnhancedUltrafiltration (MEUF), to recover and reuse the surfactant. (Lipe etal., 1996; Sabatini et al., 1998b.)

Chemical Oxidation as a Polishing Step. In the presently claimedinvention and disclosed invention, surfactant flushing is followed by apolishing stage utilizing the introduction of a chemical oxidant tosubstantially degrade the contaminant left in the soil and groundwatersubsequent to the surfactant flushing step. Bench-scale experiments wereconducted to evaluate the effectiveness of in-situ chemical oxidation inorder to illustrate and evaluate the primary performance characteristicsof the technology, including (1) oxidant-contaminant reaction kinetics,(2) matrix interactions and other secondary geochemical effects, (3)subsurface oxidant transport, (4) overall oxidant consumption, and (5)contaminants treated and overall reductions achieved

Chemical Oxidant Selection and System Design. The first step in theprocess of chemical oxidant polishing is selecting the proper oxidantfor the site. The two most common oxidants used for process applicationsare hydrogen peroxide and potassium permanganate, however sodiumpermanganate, ozone, chlorine dioxide, dissolved oxygen or any otheroxidant, in which a person having ordinary skill in the art may befamiliar, may be tested and be used in this system. To ensure asuccessful project, several design steps of a chemical oxidationpolishing system must be satisfied. An understanding of relativereaction rates and the life span of reactants are required to ensureadequate contact time for the desired reactions. The chemical demandassociated with pH adjustment must be evaluated since many of theoxidation reactions are pH-dependant. In addition, geochemicalcharacteristics of the site must be identified to help predict hownaturally occurring mineral and organic fractions within the soil andground water will affect the process.

Before installing a field-scale chemical oxidation system, certain datamust be collected to ensure proper chemical addition ratios and reactiontimes are achieved at the site. This information may include, but is notlimited to, data on the reaction kinetics, pH conditions, and naturallyoccurring interference within the subsurface for the specific site. Inaddition, mobility control and transport of the injected oxidant to thetarget areas is crucial, especially at a site with less of apermeability zone and having high organic and mineral interference.

Degradation Test. Similar to surfactant screening tests, bench-scaleoxidation degradation studies (i.e., batch tests and one-dimensionalcolumn studies) are performed in the laboratory to investigate thereaction rates and mechanisms for the previously discussed oxidantsusing soils, NAPL (if available), and contaminated groundwater collectedfrom the demonstration site. In the laboratory batch tests/kineticstudies, the samples are prepared in the reactor (e.g., 40 ml EPA vials)spiked with site contaminants (i.e., LNAPL and/or DNAPL) at thepre-determined concentrations (from high ug/L to low mg/L). These arethe typical pollutant levels observed at the dilute plume area and/orafter most NAPL mass has been removed from the contaminant source area.The Fenton's reagent and permanganate constituents required to promotethe respective oxidation reactions were added to the reactor (e.g., 40mL vials) at concentrations between 500 mg/L to ten percent. The sampleswere equilibrated for various reaction periods (from hours to days) atthe demonstration site groundwater temperature. The final contaminant(s)and oxidant concentrations were measured. Changes of reactionparameters, such as pH and redox potential, Eh, were recorded. Thereaction rate constants were calculated to quantify the removal ofcontaminant(s).

In addition, the demand for pH adjustment during chemical oxidation wasevaluated, since many of the reactions involved are pH dependent.Maintaining the proper pH conditions for Fenton's oxidation is crucialto the availability of the ferrous ion (Fe²⁺) catalyst. The buffercapacity of the soil determines whether pH adjustment for chemicaloxidation is effective and/or economical. To evaluate the effects of pH,testing was performed using potassium permanganate and Fenton's reagentunder acidic, neutral, and basic conditions. Similar batch/kinetic testsfor varying solution pH were conducted as previously described. Soil andgroundwater conditions can affect chemical oxidation performance throughdirect competition with contaminants for the oxidant and should,therefore, be taken into account.

The primary interference with Fenton's oxidation is carbonate andbicarbonate, which influence pH conditions and compete with contaminantsfor the hydroxyl radical. Elevated soil organic matters react withFenton's reagent and potassium permanganate. Oxidation of heavy metals,such as trivalent chromium (Cr(III)), remobilize the toxic form ofmetals like hexavalent chromium, Cr(VI), and therefore increase theunwanted risk at the site. If potential risk of remediation of Cr ispresent, additional tests are conducted to address these concernsdepending on the selected site conditions (e.g. Cr desoprtion test inthe soil peak columns). Typically, a phased approach is used tostreamline the tests and minimize the number of tests. This can beachieved by evaluating the degradation rates of the targeted pollutantusing the potential oxidants in a batch experiment. Only those oxidantswith favorable degradation rates will be further investigated on theirconsumption rate with the site-specific soil. The chemical oxidant withminimum mass losses to the soil is thereafter tested in aone-dimensional column or a two-dimensional sand tank in order tooptimize their conditions for complete degradation of pollutant infield. The optimal chemical oxidation system is thereafter able to beselected for the field application and is therefore site specific orsite optimized.

EXAMPLE 1 Sequent Surfactant Flushing and Chemical Oxidation for LNAPLRemediation—a Gasoline-Contaminated Underground Storage Tank (UST) Site

A particular gasoline contaminated-site is located in the southeasternOklahoma town of Golden. The main contaminant is gasoline fuel as aresult of the leakage of USTs from two former corner gas stations. Depthto the contaminated zone was 5 to 25-feet. Most free phase LNAPLs weretrapped in the shallow zone (5 to 15 ft) containing sandy silt, siltyclay, and silt. The treated area covered approximately 25,000 ft². Theprimary goal of the project was to remove all free phase gasoline. Thesecondary goal was to demonstrate a significant decrease in soil andgroundwater concentrations (one to two orders of magnitude). Thetertiary goal was to see how low the final contaminant concentration ingroundwater could be achieved, to approach the Maximum Contaminant Level(MCL).

Before field implementation, Golden site LNAPL, and soil and groundwatersamples were obtained and used to screen for the optimal surfactantsystems. In the laboratory screening experiments, four anionicsurfactant/cosurfactant mixtures were investigated for their potentialuse in remediating Golden LNAPL (fuel gasoline) with the in situsurfactant flushing technology disclosed and claimed herein. Theselected surfactant/cosurfactant included mixtures of (1) sodiumdioctylsulfosuccinate (AOT:75% active. Aerosol OT 75% PG surfactant, byCytec Industries, Inc., West Paterson, N.J., USA) and sodiumdihexylsulfosuccinate (AMA), (2) AOT and polyoxyethylene sorbitanmonooleate (Tween 80), (3) AOT and linear alkyl diphenyloxidedisulfonate (Calfax 16L-35% active, by Pilot Chemical Company, Santa FeSprings, Calif., USA), and (4) Alkylamine sodium sulfonate (LubrizolDP10052) and AMA. All surfactant solutions were prepared according totheir percent activity. For example, a 100 g 0.75% AOT solution isprepared by adding 1 g of AOT raw material (75% active) to 99 g of H₂O(water). The laboratory screening activities consisted of numerous testsincluding surfactant-NAPL phase behaviors, surfactant sorption andprecipitation, and contaminant extraction-column studies as describedpreviously in the experiment methodology section (also see Shiau et.al., 1994; Shiau et. al. 1995; Shiau, et. al. 2000). As shown in Table1, batch surfactant screening experiments indicate that all foursurfactant mixtures used can achieve Winsor Type III (middle-phase)microemulsion with Golden site NAPL, mostly at total surfactantconcentration less than 1 wt %. TABLE 1 Summary of Surfactant/NAPL PhaseBehaviors NAPL (TPH) solubility Equilibrated Surfactant at optimal Timeof Stable Concentration Appearance of Type III Type III Evaluated WinsorType III system Microemulsion¹ Surfactant System wt % Microemulsion mg/L(hr) AOT/AMA   1 to 2 transparent 440,000 1 to 2 AOT/Tween 80 0.2 to 1translucent 400,000  8 to 12 AOT/Calfax16L-35² 0.2 to 1 translucent450,000 1 to 2 Lubrizol DP/AMA³ 0.2 to 1 opaque 400,000  8 to 12¹NaCl (ranging from 0.1 to 3 wt %) was used to achieve the optimal TypeI system at various ratios of surfactant mixtures²Surfactant system used at Golden UST site³A small portion of the contaminated zone was treated with thissurfactant

Table IA illustrates the formulation of the preferred surfactant systemAOT/Calfax 16L-35 used at the Golden site for gasoline clean-up. Alsosurfactant formulations for other conatminants, such as disel fuel andTCE, are also listed in Table IA. TABLE IA Surfactant CosurfactantElectrolyte Type of Contaminants wt % wt % wt % Microemulsion GasolineDioctylsulfosuccinate sodium linear NaCl Winsor Type III (AOT) alkyl 1.20.75 diphenyloxide disulfonate (Calfax 16L- 35) 0.19 Diesel Fueldioctylsulfosuccinate sodium linear NaCl Winsor Type III (AOT) alkyl 1.70.75 diphenyloxide disulfonate (Calfax 16L- 35) 0.19 TCEDioctylsulfosuccinate sodium linear NaCl Winsor Type III (AOT) alkyl1.84 0.77 diphenyloxide disulfonate (Calfax 16L- 35) 0.27

The screening tests were conducted at different surfactant/cosurfactantratios by adding various amounts of NaCl to promote the formation of amiddle-phase (or Winsor Type III) microemulsion. In these tests, a lowsurfactant concentration (<1 wt %) approach was found to significantlyimprove the cost effectiveness of the site clean-up effort. Based on thescreening tests, it was concluded that one surfactant system was thebest candidate for the site-specific conditions (i.e., able to produce atranslucent middle-phase microemulsion with ultra-low interfacialtension at value <0.005 dyne/cm and the highest NAPL solubility): acombination of anionic surfactant mixture, AOT/Calfax 16L-35 (totalconcentration=0.94 wt %) at AOT/Calfax weight ratio of of 0.75/0.01 gwith 1.2% NaCl added. The prepared formulation is shown in Table IA.

For the polishing step, abiotic chemical oxidation was used to treat theresidual oil and dilute plume at the shallow zone of this site theGolden site. Both Fenton's Reagent and potassium permanganate wereevaluated. As shown in Table 2, at a low concentration of chemicaloxidant, Fenton's Reagent appeared to be more favorable in treating theBTEX compounds found at the site. TABLE 2 Representative Results of BTEXDegradation with Fenton's Reagent Fenton's Benzene¹ % Toluene %Ethylbenzene % m,p-Xylene % o-Xylene % Reagent Used reduction reductionreduction reduction reduction H₂O₂ = 2,000 mg/L 92 44 59 47 44 Fe⁺² = 90mg/L pH = 2 to 3 adjusted by 50% H₂SO₄ H₂O₂ = 2,000 mg/L 93  NA² NA NANA Fe⁺² = 90 mg/L pH = 2 to 3 adjusted by 50% H₂SO₄ ² KMnO₄ = 5,000mg/L³ 8 NA NA NA NA¹Initial BTEX mixtures containing 1,000 ug/L of individual compound;reaction time = 12 hr²Initial benzene-only concentration = 4,000 ug/L; NA = not available³Initial benzene-only concentration = 1,000 ug/L

For example, 93% of the initial 4,000 μg/L benzene was degraded using aFenton's Reagent, containing H₂O₂, 2,000 mg/L, Fe⁺², 90 mg/L, pH value @2 to 3. Benzene degradation was only 8% of the initial 1,000 μg/Lbenzene after a 5,000 mg/L KMnO₄ solution was added.

As shown in Table 3, one-dimensional column tests were conducted toassess the contaminant removal under hydrodynamic condition. Injectionof a one pore volume of AOT/Calfax (0.94%) mixture was able tomobilize >90% of the trapped LNAPL from the 1-D column. TABLE 3 Summaryof 1-D Column Study Results Post- Post-surfactant surfactant + chemoxid(Step 1) (Step 2) Total % contaminant % contaminant contaminant ProcessUsed removed removed removal % Step 1: 91¹ 8.6² 99.6² Surfactant:AOT/Calfax (0.94 wt %) + NaCl 1.2 wt % (1PV) Step 2: Fenton's Reagent:H₂O₂ (0.4 wt %) Fe⁺² (90 mg/L) pH = 2.6¹Estimated based on the mobilized NAPL volume and dissolved NAPL data;initial column oil saturation = 2%²Based on final soil extraction measurement

Fenton's Reagent was selected to polish the residual NAPL after thesurfactant flood. Representative column results are shown in FIG. 2 andTable 3. In the soil column, the total NAPL removed (measured by totalpetroleum hydrocarbon, TPH, or gasoline range organics, GRO) was 99.6%.Without the polishing step (chemical oxidation), the surfactant flushingalone could not achieve remediation to an extremely low contaminantlevel in the soil. Direct injection of a high concentration Fenton'sReagent (H₂O₂ level at 10 wt %) would have required multiple porevolumes (>5 PV) to achieve 80% to 90% contaminant removal (data notshown). Therefore, laboratory experiments indicated that integratedsurfactant flushing followed by chemical oxidation would be able totreat the Golden site NAPL to extreme low level concentrations (low ppbrange).

In situ surfactant flushing was used to recover free phase LNAPL(gasoline) using the low concentration surfactant (<1 wt %) andpolishing oxidant methodology of the presently disclosed and claimedinvention. One pore volume of 0.94 wt % AOT-Galfaxl6L-35 (Table IA)surfactant (190,000 gallons) was injected into the contaminated shallowzone (source area, mostly silty material) over a two month period tomobilize the trapped NAPL. Initial free phase gasoline thickness on thewater table ranged between 2.7 feet to 3.3 feet. Representative resultsfrom the field remediation effort at the Golden UST site are shown inFIGS. 3 and 4 and in Tables 4 and 5. TABLE 4 Representative ContaminantConcentration in Golden Soil before and after the Sequent SurfactantFlushing and Chemical Oxidation Soil Sample Comparison Data Pre-Flushvs. Post Flush Calfax/AOT Flush Percent Percent Sample Depth BenzeneToluene Ethylbenzene Xylenes TPH-Gro Reduction Reduction Number ft. bgl.ug/kg ug/kg ug/kg Ug/kg mg/kg Benzene TPH-Gro MLS-1A 12.5 13400.058100.0 18800.0 92700.0 809.0 PTGP-2A 12.5 511.0 9970.0 3520.0 20600.0164.0 96.2 79.7 MLS-1B 14.0 16000.0 185000.0 85300.0 454000.0 3630.0PTGP-2B 14.0 2350.0 37300.0 14600.0 78600.0 548.0 85.3 84.9 MLS-2A 12.531800.0 438000.0 114000.0 595000.0 5080.0 GP-7A 12.5 2400.0 41800.017100.0 95700.0 691.0 PTGP-9A 12.5 225.0 476.0 ND ND 56.0 99.3 98.9MLS-2B 14.0 4980.0 26700.0 6640.0 38100.0 345.0 PTGP-9B 14.0 284.0 ND527.0 3790.0 59.0 94.3 82.9 DW-1A 11.0 1900.0 14900.0 8750.0 48400.0355.0 PTGP-1A 11.0 ND ND ND ND 4.2 >99 98.8 DW-1B 14.0 11200.0 99800.044900.0 250000.0 2190.0 PTGP-1B 14.0 2670.0 4920.0 7580.0 28400.0 137.076.2 93.7 DW-5A¹ 14.0 20800.0 148000.0 58800.0 326000.0 2780.0 GP-6B14.0 1210.0 12720.0 5820.0 31900.0 325.0 94.2 88.3 DW-8A 14.0 41100.0182000.0 54600.0 277000.0 2560.0 PTGP-10A 14.0 1060.0 42700.0 19700.0104000.0 890.0 97.4 65.2 DW-16A¹ 11.0 9720.0 277000.0 129000.0 707000.05740.0 PTGP-12A 11.0 ND 118.0 ND ND 19.0 >99 99.7Notes:Background Concentration¹The 14 foot sample for DW-5A and DW-16A denotes the 14 foot depth,unlike DW-1A.

TABLE 5 Oklahoma Corporation Commission (OCC)/U.S. EnvironmentalProtection Agency (U.S. EPA) Post Test Soil Sample ResultsConcentration, mg/kg Sample Depth ethyl- I.D. Ft. bgl. benzene Toluenebenzene xylenes TPH-Gro PB-1 15.8 0.425 1.93 1.12 4.29 88.3 PB-2 16.70.103 0.170 0.035 0.190 1.83 PB-2 18.5 2.27 8.07 2.390 13.4 111.0 PB-317.7 0.295 3.02 1.20 6.87 54.5 PB-3 18.5 0.165 0.374 0.054 0.299 2.40PB-4 17.0 4.24 16.7 4.14 21.6 155 PB-5 10.2 0.072 0.675 0.28 1.86 18.8PB-5 17.3 0.727 6.31 2.18 13.1 160.0

No visible or instrumental evidence of free phase gasoline was detectedin 25 recovery and monitoring wells (three out of 28 wells had minimalthicknesses) during the post surfactant sampling event (FIG. 3). Theobserved benzene concentration indicated that 75%-99% reduction in soilconcentrations were achieved during the surfactant flush (FIG. 4 andTable 4). Similarly, a reduction of TPH (GRO) concentrations in thesoils was between 65%-99%. After surfactant flushing, the remainingtrace residual and dissolved NAPL were treated by the final polishingsteps using chemical oxidation in the shallow zone, where most NAPL waspresent before the surfactant flushing. Representative soilconcentrations after the post-oxidation phase are summarized in Table 5.As shown in Tables 4 and 5, further contaminant reduction/degradation(OCC/EPA soil sampling event held in June, 2002) was observed after thepost-polishing step was completed. These results indicate that theintegrated surfactant flushing and chemical oxidation methodology of thepresently disclosed and claimed invention is capable of remediatingcontaminants to substantially non-detected or extremely low level, ifnot completely removed, in a “real world” field-scale test.

EXAMPLE 2 Sequent Surfactant Flushing and Chemical Oxidation Polishingfor DNAPL—a TCE-Contaminated Site

The targeted site was contaminated by TCE, a DNAPL and common degreaser.The main focus of this experiment was to treat the dilute TCE plume withan in-situ chemical oxidation process. This approach was selected ratherthan treating the source zone NAPL because the DNAPL source zones couldnot be identified. Most laboratory efforts were focused on evaluatingthe effectiveness of two selected oxidants, potassium permanganate(KMnO₄) and Fenton's reagent, for TCE and cis-DCE degradation. A limitedeffort was given to evaluate the effectiveness of sequent surfactantflushing and chemical oxidation to treat the TCE-contaminated source (orhot) zone.

Use of Potassium Permanganate for TCE/DCE Degradation

Batch experiments were conducted to evaluate the degradation rates ofTCE, cis-DCE, or their mixture by KMnO₄. These experiments were carriedout in TCE/DCE dissolved solutions in the absence (Table 6) or presence(Table 7) of site-specific soil. As shown in Table 6, 250 mg/L KMnO₄ candegrade TCE or DCE completely at low contaminant levels. Initialcontaminant concentrations ranged from several hundred of ug/L to morethan 100 mg/L. As shown in Table 7, KMnO₄ concentrations ranging from 10mg/L up to 10,000 mg/L (1%) solution were tested. Results indicated thatmost reactions between KMnO₄ and TCE, DCE, and TCE/DCE mixtures (betweenfew hundreds ppb to 5 ppm) were complete after a 24-hr reaction period.TABLE 6 Degradation Reaction of KMnO₄ and low level of TCE, DCE andtheir mixtures without soil Final Final KMnO4 TCE DCE added, TCE, % DCE% Sample ID ug/L ug/L mg/L degraded degraded DCE-C-8 8 4820 0 NA 0(control) DCE-100-8 3 691 100 NA 85.7 DCE-250-8 0 22 250 NA 99.5 TCE-C-8283 0 0 0 NA (control) TCE-100-8 0 1 100 100 NA TCE-250-8 0 1 250 100 NAD&T-C-8 70 1407 0 0 0 (control) D&T-100-8 0 14 100 100 99.0 D&T-250-8 011 250 100 99.2Note:-8 samples were analyzed after 29 hrs of sample preparation.

TABLE 7 Degradation Reaction of KMnO₄ and TCE, DCE and their mixtureswith two types of soil (Soil 1-26′-27′; Soil 2-18′-20′, in 40 mLsolution) Final Final KMnO₄ TCE DCE added TCE % DCE % Sample ug/L ug/Lmg/L degraded degraded SDCE-C 18 5486 0 NA 0 SDCE-100 0 17 100 NA 99.7SDCE-250 0 16 250 NA 99.7 STCE-C 237 0 0 0 NA STCE-100 0 0 100 100 NASTCE-250 0 0 250 100 NA ST&D-C 117 2432 0 0 0 ST&D-100 0 13 100 100 99.5ST&D-250 0 12 250 100 99.5

Most reactions between KMnO₄ and TCE/DCE are completed in less than onehour under room temperature (20° C.). As shown in Table 8, experimentsconducted with soil added indicate that complete degradation of TCE andDCE was observed under similar conditions. TABLE 8 Degradation Reactionof KMnO₄ and high level of TCE without soil Initial KMnO₄ Final TCEadded TCE Sample ID mg/L mg/L % degraded Control 343 0.0 0 T10000 0.010,000 100 T5000 0.0 5,000 100 T1000 0.0 1,000 100 T500 111 500 67.7

The loss of KMnO₄ in two soil samples collected from the site weredetermined to be negligible during 4-, 7-, and 14-days of reactionperiod (data not shown). Low sorption loss of KMnO₄ reduced the amountof KMnO₄ required and the total cost of remediation project.

Under higher initial TCE levels (>300 mg/L), results indicate thatadding 1,000 mg/L or more KMnO₄ completely degraded the added TCE. A67.7% reduction of TCE was observed with 500 mg/L of KMnO₄ solution.

Batch study indicated that addition of potassium permanganate degradeddissolved TCE and DCE in the dilute plume near the vicinity of the soilsampling locations. In addition, other loss mechanisms for permanganateincluding sorption and fortuitous reactions with other reduced compoundswere minimal in the tested samples.

Use of Fenton's Reagent for TCE/DCE Degradation

Fenton's reagent is the second oxidant tested. Fenton's reagent wasprepared by dissolving H₂O₂ and catalysis Fe(II) (FeCl₂ or FeSO₄) inacidic solution (HCl or H₂SO₄).

Batch results indicated that Fenton's reagent degrades both TCE and DCE,but appears less efficient compared to KMnO₄ on a weight basis. Forexample, 283 ug/L TCE can be completely degraded by 100 mg/L KMnO₄solution, yet 100 mg/L H₂O₂/FeCl₂ solution only oxidize 51.7% of TCE.For similar contaminant concentrations, DCE degradation required moreFenton's reagent than TCE. Note that some pollutants, such astrichloroethane (TCA) or BTEX, could not be completely degraded byKMnO4, but will be degraded effectively by Fenton's reagent.

The batch studies clearly indicate that both KMnO₄ and Fenton's reagentwere candidates for degrading the target contaminant, TCE, and thecommon intermediate, DCE, at the selected sampling locations at theDNAPL-impacted site.

1-D Column Study with KMnO₄-Only for TCE Removal

Several column tests were conducted by injecting KMnO₄ at differentconcentrations (100, 500, 5000, 20000 mg/L) under various TCE residualsaturation in the soil packed column. In the column study, fifteen totwenty five pore volumes of KMnO₄ were injected to evaluate the removalof TCE under the hydrodynamic conditions.

At a 1% initial TCE residual saturation, significant gas bubbles (mainlyCO₂ gas) were observed in the effluent after a 5,000-mg/L KMnO₄ solutionwas injected, while TCE concentration also began to drop significantly(to less than 10 mg/L level). In another column test, a 10% TCE residualsaturation was used with various KMnO₄ levels being injected (100, 500,5,000, 20,000 mg/L). Similarly, numerous gas bubbles were created whenhigher KMnO₄ concentrations were injected (5,000 mg/L and above) (datanot shown). In addition, dark brown MnO₂ precipitates were accumulatedat various locations in the column.

After the KMnO₄ flushing, the treated column was dismantled and the soilwas extracted with methanol to determine the final TCE concentration.The final TCE concentrations in the column ranged from 8 mg/Kg to 47mg/Kg in different columns (both low and high initial TCE levels). Asignificant amount of TCE was degraded with KMnO₄ flushing. However, asignificant release of CO₂ near the NAPL source area could potentiallychange the hydraulic permeability of the aquifer and lead to by-passaround the TCE ganglia preventing further removal, as other researchershave suggested. In addition, significant accumulation of MnO₂precipitates at the interface of NAPL and water also reduce the masstransfer of KMnO₄ to TCE and decrease the TCE degradation rate. Thisproblem has been observed in field trials with KMnO₄ and is a limitationof the technology for remediation of contaminated hot zone. Results fromthese column tests indicate that injection of KMnO₄ alone couldeffectively degrade TCE under proper conditions, such as for aTCE-impacted dissolved plume but not in areas with free phase DNAPL orhigh level of TCE residual saturation. Chemical oxidation is veryeffective for degrading a TCE dilute plume or as a polishing-step forsource zone remediation after the majority of the TCE is removed by thesurfactant flooding. The relatively low quantity of remaining TCE wouldbe less likely to cause manganese precipitation and hydraulic bypassingupon reaction with KMnO₄.

1-D Column Study with Sequent Surfactant Flushing and Chemical Oxidation(KMnO₄) Flushing for TCE Removal

Additional column tests were conducted using surfactant flushing tofirst remove significant TCE NAPL mass, followed by KMnO₄ flushing todegrade the TCE left in the column. Examples of the column study resultsare shown in FIG. 5. Initial TCE residual saturation was 2%. At 4 PV, asurfactant solution, containing 2.5% dihexyl sulfosuccinate (AMA), 5%diphenyl oxide disulfonate (Calfax), 3% NaCl, and 1% CaCl₂, was injectedinto the column. The selection of this surfactant system was based on aprevious field test done for a mixed DNAPL contaminated site, containingtricholorethane (TCA), TCE, DCA, and DEC. The enhancement of TCAsolubility with the selected surfactant system (Calfax/AMA/CaCl₂/NaCl)is listed in Table 9. TABLE 9 Comparison of Trichloroethane (TCA)Solubilization in Batch and Column Studies Maximum TCA TCA Solubilizedin Solubilized in column Surfactant System Batch test (mg/L)¹ test(mg/L) Dowfax/AMA/NaCl/CaCl₂  99,259 168,996 Lubrizol71/IPA/NaCl/259,355 NA³ CaCl₂¹Volume determined by volumetric addition of TCA during the phasebehavior study²Surfactant used in the sequent surfactant flushing/chemical oxidationtest³NA = not available

A surfactant system used for TCA could be used for TCE (with similarhydrophobicity property) to produce a middle-phase microemulsion.Therefore, a mixture of Calfax/AMA surfactant was used to conduct this1-D column test. Significant TCE mass (concentration reached 100,000mg/L) was removed from the column after surfactant breakthrough. After 5PV of surfactant flushing, a 2,000 mg/L KMnO₄ solution was injected tofurther degrade the TCE in the column. A total of 4 PV of KMnO₄ solutionwas injected in the column before post-water flushing began at 12 PVinjection time.

Significant TCE mass was removed during the surfactant flushing period.A decrease of the TCE concentration, eventually below the quantificationlimit, after the KMnO₄ breakthrough, is also clearly demonstrated. Postcolumn extraction indicated that 99.94% of the initial TCE was removedfrom the column. Note that the surfactant concentration used in thiscolumn test was 7.5 wt %. As shown in Table 10, a recent batch studyconducted by Applicant indicates that a low surfactant concentration (<1wt %) could achieve similar solubility enhancement for TCE. TABLE 10Solubilozation of DNAPL (TCE) Using Low Surfactant Concentration (1 wt%) TCE Solubilized Sample in bacth test Note Name Phase mg/L 1 wt %surfactant fb-015s middle 177104 Calfax/AOT fb-015s aqueous 99577Calfax/AOT fb-014s middle 383813 Calfax/AOT fb-014s aqueous 66677Calfax/AOT fb-008 aqueous 152882 Lubrizol System

Therefore, a surfactant flushing with a low surfactant concentrationsystem (e.g., Calfax/AOT—see Table IA for TCE) followed by a chemicaloxidation step significantly improves the state of the art and makes ittechnologically and economically viable to completely remediatecontaminated sites.

Although the present invention has been described in considerable detailwith reference to certain preferred versions thereof, other versions arepossible. For example, single surfactant systems such as anionic/anionicand nonionic/nonionic mixtures; surfactant systems such asanionic/cationic and anionic/nonionic mixtures; and contaminants such aspolyaromatic hydrocarbons (PAH), creosote, crude oil, pesticides,polychorinated biphenyls (PCBs) and ketones can be utilized with thisintegrated approach. Therefore, the spirit and scope of the appendedclaims should not be limited to the description of the preferredversions contained herein.

REFERENCES

The following references, to the extent that they provide exemplaryprocedural or other details supplementary to those set forth herein, arespecifically incorporated herein by reference in their entirety asthough set forth herein in particular.

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Knox, R. C., Shiau, B. J., Sabatini, D. A., and Harwell, J. H., 1999.“Field demonstration studies of surfactant-enhanced solubilization andmobilization at Hill Air Force Base, Utah,” in Innovative SubsurfaceRemediation, Field Testing of Pysical, Chemical, and CharacterizationTechnologies, Brusseau, M. L., Sabatini, D. A., Gierke, J. S., Annable,M. D. (eds.), ACS symposium series 725, 49-63, American ChemicalSociety, Washington DC.

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1. A method for substantially removing subsurface contaminants,comprising the step of introducing an effective amount of a mixture ofsodium dioctylsulfosuccinate, linear alkyl diphenyloxide disulfonate,and water, wherein the weight percent of the sodiumdioctylsulfosuccinate and linear alkyl diphenyloxide disulfonate in themixture is in a range from about 0.05% to about 15% by weight of themixture.
 2. The method of claim 1, wherein the subsurface contaminant isa dense non-aqueous phase liquid.
 3. The method of claim 1, wherein thesubsurface contaminant is a light non-aqueous phase liquid.
 4. A methodfor substantially removing subsurface contaminants, comprising the stepof introducing an effective amount of a mixture of sodiumdioctylsulfosuccinate, linear alkyl diphenyloxide disulfonate, andwater, wherein the weight percent of the sodium dioctylsulfosuccinateand linear alkyl diphenyloxide disulfonate in the mixture is in a rangefrom about 3% to about 8% by weight of the mixture.
 5. The method ofclaim 4, wherein the subsurface contaminant is a dense non-aqueous phaseliquid.
 6. The method of claim 4, wherein the subsurface contaminant isa light non-aqueous phase liquid.
 7. A method for substantially removingsubsurface contaminants, comprising the step of introducing an effectiveamount of a mixture of sodium dioctylsulfosuccinate, linear alkyldiphenyloxide disulfonate, and water, wherein the weight percent of thesodium dioctylsulfosuccinate and linear alkyl diphenyloxide disulfonatein the mixture is in a range from about 1% to about 3% by weight of themixture.
 8. The method of claim 7, wherein the subsurface contaminant isa dense non-aqueous phase liquid.
 9. The method of claim 7, wherein thesubsurface contaminant is a light non-aqueous phase liquid.
 10. A methodfor substantially removing subsurface contaminants, comprising the stepof introducing an effective amount of a mixture of sodiumdioctylsulfosuccinate, linear alkyl diphenyloxide disulfonate, andwater, wherein the weight percent of the sodium dioctylsulfosuccinateand linear alkyl diphenyloxide disulfonate in the mixture is in a rangefrom about 0.05% to about 1% by weight of the mixture.
 11. The method ofclaim 10, wherein the subsurface contaminant is a dense non-aqueousphase liquid.
 12. The method of claim 10, wherein the subsurfacecontaminant is a light non-aqueous phase liquid.